The Pediatric HIV AIDS Cohort Study (PHACS) addresses two important research questions: (1) Is there a risk to fetuses who are exposed to antiretroviral (ARV) drugs taken by their HIV-1-infected mother during pregnancy; and (2) What is the clinical course of children with perinatal HIV infection as they age through adolescence towards adulthood. These questions are being addressed through three separate protocols being conducted at 21 PHACS clinic sites in the US including Puerto Rico. The specific aim of the SMARTT Study is to define the short and long-term safety of ARV exposure among HIV-exposed but uninfected infants. To accomplish this, HIV-uninfected children born to infected mothers are evaluated prospectively in order to identify abnormalities of growth, development, language, hearing, cardiac and neurologic function, and other organ systems. Children with abnormalities are further evaluated to determine if these abnormalities are associated with exposure to specific ARVs. Other causes of the abnormalities are also investigated. This information will help in deciding which ARVs are safest for a woman to take during pregnancy - both for her own treatment and to prevent infection of her child. The specific aims of the AMP study are, among pre-adolescents and adolescents with perinatal HIV infection: (1) To define the impact of HIV infection and ARVs on their growth and development; sexual maturation; development of risk factors for cardiovascular disease; cognitive, academic, vocational, sexual, and social functioning; mental health; and risk taking behavior including substance use; (2) To identify infectious and non-infectious complication of HIV and ARV therapy, including end organ disease (neurologic, renal, pulmonary, bone) and nutritional and metabolic abnormalities; and (3) to study genetic, virologic (including antiretroviral resistance), and immunologic factors whic alter the course of HIV infection and its response to treatment. A second study, AMP Up, allows the AMP participant to be followed into adulthood once they turn 18 years of age, utilizing a less intensive study design that combines both in-person visits and on-line data collection. Since youth with perinatal HIV are now reaching adulthood, an important goal of AMP Up is to learn about their transitioning to adulthood and adult medical care. Since pediatric HIV is now a chronic disease, an understanding of the long-term outcomes of HIV infection and its treatment is necessary to provide them with optimal long-term care. In all studies, participants are evaluated prospectively according to a standard protocol. Both utilize a strategy of triggered evaluations, with specific abnormal findings leading to more intensive evaluations to further characterize the abnormality. Repository specimens are collected to allow for additional biochemical and genetic testing.